While the magnetizable coatings of virtually all magnetic recording media now in use comprise magnetizable particles dispersed in organic binder, the amount of information that can be recorded on any such medium is reaching the theoretical limit. It is known that information can be recorded more compactly on metallic thin-film magnetic recording media. Such media may be used in perpendicular recording when they have an easy axis of magnetization perpendicular to the surface of the recording layer (see U.S. Pat. No. 4,210,946).
A major problem with metallic thin-film magnetic media is their susceptibility to wear. Record/playback transducer heads contacting the metallic thin film will have a tendency to erode or otherwise damage the film. Even slight erosion will result in considerable loss of data when high bit density recording is employed. Applications involving erosion and severe wear of metallic thin film magnetic media are on the increase, with video tape and electronic cameras being two examples.
Thus, such media require some sort of protective covering. This covering, known as the lubricant or top coat, functions to: lubricate, add corrosion protection, and give wear resistance to the magnetic medium. Among the wide variety of lubricants developed for magnetic media are fluorinated polyethers (e.g. see U.S. Pat. Nos. 3,778,308, 4,267,238 and 4,268,556).
The lubrication or top coat layer should be firmly anchored to the magnetic recording layer so that it will not be removed or cause clogging of the recording or playback heads. In most cases in the prior art, it is believed that the fluorinated lubricants have been applied as coatings from halogenated solutions or emulsions with no means, other than physical absorption or adsorption, of bonding the lubricant to the magnetic recording medium.
Commonly assigned U.S. Pat. No. 4,404,247 discloses a protective covering for magnetic recording media comprising: a. an inner layer of film forming aromatic or heterocyclic polymerizable monomer and vinyl aromatic comonomer, and b. an outer layer of a compound containing perfluoropolyether segments. The above materials are applied in solution to magnetic recording media in two discrete coating steps and are subsequently in-situ polymerized. The contiguous monomers of the two layers are said to copolymerize, bonding the perfluoropolyether segments to the magnetizable coating through the inner layer. The perfluoropolyether lubricant is said to have a significantly greater adherence to the metallic thin-film magnetizable recording medium than it would have if it had been directly applied, because of the inner layer material.